This application claims the priority of Korean Patent Application No. 2002-17599, filed Mar. 30, 2002 in the Korean Intellectual Property Office, which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a planar optical waveguide-type optical transceiver module and a manufacturing method thereof, and more particularly, to an optical waveguide platform for mounting an optical device by a flip chip bonding method and a manufacturing method thereof.
2. Description of the Related Art
An optical device of a planar optical waveguide manufactured on a substrate, for example, a silicon substrate, by a flame hydrolysis deposition (FHD) method or a plasma enhanced chemical vapor deposition (PECVD) method, functions as a passive optical device. However, the optical device cannot function as a light emitting device, such as a laser diode (LD), a light receiving device, such as a photo diode (PD), nor any other active optical device that has electro-optical functions or active optical functions. Accordingly, in order to perform optical switching, optical exchanging, optical signal transmitting, and optical signal receiving functions, a separate active device chip has to be hybrid mounted with an optical waveguide device, so as to perform both the passive optical function of an optical waveguide and the active optical function of a semiconductor active device. In this case, it is necessary to make a small-sized active optical device in the form of a chip, using a semiconductor technique, and to precisely align and mount the active optical device on an optical waveguide device, so as to reduce optical contact loss. Accordingly, an optical waveguide platform for mounting an active optical device by a proper method, such as a flip chip bonding method, is required.
FIGS. 1A through 1G are sectional views illustrating a conventional method of manufacturing an optical waveguide platform. A terrace 12 is formed on a silicon substrate 10 by an anisotropic etching method, as shown in FIG. 1A. Thereafter, a lower clad layer 14 formed of a silica layer is formed on the silicon substrate 10 having the terrace 12. Here, a step is formed on the surface of the lower clad layer 14 by the step of the terrace 12, as shown in FIG. 1B.
In order to remove the step on the surface of the lower clad layer 14, which is formed by the step of the terrace 12, the lower clad layer 14 is polished. Thus, a planarized lower clad layer 14a is formed, as shown in FIG. 1C. Next, a core layer 16 is formed on the planarized lower clad layer 14a and etched into a waveguide pattern. An upper clad layer 18 is formed on the core layer 16, as shown in FIG. 1D.
Subsequently, the upper clad layer 18, the core layer 16, and the planarized lower clad layer 14a are dry etched to expose the terrace 12. Accordingly, referring to FIG. 1E, a portion through which the terrace 12 is exposed becomes a trench 19 in which an optical device will be mounted. A dielectric layer 20 is formed on the floor of the terrace 12, and under bump metal (UBM) layers 22 for forming electrodes and a solder pad are deposited on the dielectric layer 20 and on a portion of the upper clad layer 18, as shown in FIG. 1F.
Thereafter, solder is deposited on a solder pad formed of the UBM layers 22 to mount an optical device 24, which is formed of a semiconductor chip, such as an LD or a PD. Then, a metal wire 26 connects the UBM layer 22 for forming an electrode, as shown in FIG. 1G.
The conventional method for manufacturing an optical waveguide platform shown in FIGS. 1A through 1G requires a silicon precision process for forming the terrace 12 and a polishing process for polishing a silica layer composed of the lower clad layer 14 due to the step of the terrace 12.
In this case, the silicon precision process for forming the terrace 12 has various restraints, such as requiring a photolithography process that uses a separate mask and being impossible to process a precise pattern when a crystal direction is wrong.
In addition, since the silica layer forming the lower clad layer 14 has a thickness of tens of xcexcm, the lower clad layer 14 is difficult to be precisely polished. Moreover, when there is non-uniformity in polishing thickness, part of the resulting optical waveguide may be unusable.
In particular, in the case of a general silica optical waveguide device, a difference in the thermal expansion coefficients of a silica layer and the silicon substrate 10 causes the silicon substrate 10 to warpage. Therefore, it is impossible to precisely polish a lower clad layer 14 without variation in the polishing thickness. As a result, the conventional method requires an additional process, such as thermal treatment for eliminating warpage of the silicon substrate 10.
FIGS. 2A through 2G are sectional views illustrating a second conventional method of manufacturing an optical waveguide platform. A lower clad layer 32 and a core layer 34 are sequentially staked on a silicon substrate 30, as shown in FIG. 2A. Portions of the core layer 34 and the lower clad layer 32 are selectively dry etched to a predetermined depth to form a trench 36 in which an optical device will be mounted. In this case, the etch depth has to be finely adjusted to enable vertical alignment between the optical output of the optical device and the core layer 34. Consequently, a fine waveguide pattern formed of a core layer pattern 34a and a lower clad layer pattern 32a having widths of several xcexcm is exposed for a considerable height, as shown in FIG. 2B.
Thereafter, an etch stopper pattern 38 is formed on the lower clad layer pattern 32a in the trench 36, as shown in FIG. 2C. Then, an upper clad layer 40 is deposited on the entire surface of the substrate 30 having the etch stopper pattern 38 and the core layer pattern 34a, as shown in FIG. 2D.
By selectively etching the upper clad layer 40 in the trench 36 region, an upper clad layer pattern 40a, which exposes the etch stopper pattern 38, is formed as shown in FIG. 2E. A metal layer 42 for supplying power for driving the optical device is formed on the etch stopper pattern 38 in the trench 36 as shown in FIG. 2F. Subsequently, solder is deposited on the metal layer 42 to mount an optical device 44 formed of a semiconductor chip, such as an LD or a PD, by a flip chip bonding method, as shown in FIG. 2G.
As described with reference to FIGS. 2A through 2G, the second conventional method of manufacturing an optical waveguide platform forms the etch stopper pattern 38 after the core layer pattern 34a is formed. In this case, the fine optical waveguide pattern having a width of several xcexcm may be damaged by a mechanical impact, such as contact with a mask, in a lithography process for forming the etch stopper pattern 38. In addition, in the case of forming the etch stopper pattern 38 by the lithography method, the heights of the upper surface of the core layer pattern 34a which the mask contacts and the etch floor on which the etch stopper pattern 38 is formed become different. Accordingly, defocus occurs in a contact aligner, thereby resulting in the formation of an imprecise etch stopper pattern. In particular, an align key for aligning and mounting the optical device cannot be precisely formed so that it is difficult to precisely align and mount the optical device.
Moreover, in order to perform the second conventional method of manufacturing the optical waveguide platform as shown in FIGS. 2A through 2G, the etch depths of the core layer 34 and the lower clad layer 32 have to be precisely adjusted to vertically align the optical device and the waveguide. In addition, in etching the upper clad layer 40, the etch depth has to be precisely adjusted until the etch stopper pattern 38 is exposed.
To solve the above-described problems, it is an objective of the present invention to provide an optical waveguide platform that is manufactured by a simple process without requiring etching a silicon substrate or polishing a silica layer.
It is another objective of the present invention to provide a method of manufacturing an optical waveguide platform without damaging an optical waveguide by forming a terrace while etching a trench without anisotropically etching a silicon substrate.
To accomplish the objectives of the present invention, an optical waveguide platform comprises a substrate, a lower clad layer formed on the substrate to have a terrace at a predetermined portion for mounting an optical device, an etch stopper pattern formed on the terrace, a height adjustment layer formed on the lower clad layer without the terrace and the etch stopper pattern to perform precise vertical alignment between the optical device and an optical waveguide by controlling the thickness of the height adjustment layer, an optical waveguide core layer and an upper clad layer sequentially formed on the height adjustment layer, and a metal layer formed on the floor of the terrace, on which the optical device is mounted.
Here, it is preferable that the etch stopper pattern is formed of a material that is not etched in etching silica. The etch stopper pattern may be formed of a chrome oxide layer. It is preferable that the height adjustment layer is formed of a silica layer or a glass layer that has a refractive index similar to that of the lower clad layer. The metal layer may be formed by sequentially forming Ti/Pt/Au or Ti/Ni/Au metal.
To accomplish another objective of the present invention, in a method of manufacturing an optical waveguide platform, a lower clad layer is formed on a substrate and an etch stopper pattern is formed on the lower clad layer. A height adjustment layer is formed on the etch stopper pattern and the lower clad layer and a core layer is formed on the height adjustment layer and patterned to form an optical waveguide pattern. Thereafter, an upper clad layer is formed on the entire surface of the substrate having the optical waveguide pattern. The upper clad layer, the core layer, the height adjustment layer, and the lower clad layer are selectively etched to expose the etch stopper pattern and form a terrace on which an optical device will be mounted. A metal layer and a solder pattern are formed on the floor of the terrace, on which the optical device is mounted.
Here, the etch stopper pattern can be formed of a chrome oxide layer, which is formed by patterning and oxidizing a chrome layer. An align key for aligning the optical device can be formed with the etch stopper pattern. The height adjustment layer can be formed of a silica layer or a glass layer by performing a plasma enhanced chemical vapor deposition (PECVD) method, a low pressure chemical vapor deposition (LPCVD) method, or a sol-gel method. In addition, the height adjustment layer can be formed by a flame hydrolysis deposition (FHD) method and formed with the core layer by controlling the amount of sources for adjusting a refractive index.
The optical waveguide platform according to the present invention can mount the optical device without processing the silicon substrate and prevents defocus in a photolithography process caused by a step, so as to prevent damage to a fine waveguide pattern. In addition, with the optical waveguide platform of the present invention, the characteristics of the optical waveguide device can be examined before etching the trench.